Apparatus for feeding fiber material into a chute

ABSTRACT

The fiber material is directed onto one or more chutes from a pneumatic transporting duct by rotatable cylinders. Each chute has a cylinder associated therewith which at least partially interrupts the transporting air stream to intercept and direct a portion of the air flow and entrained fibers into the chute. The cylinders may be positively rotated or freely mounted. The cylinders are also mounted close to the back wall of the chute to allow removal of accumulations of fibers on the cylinders.

United States Patent 1191 Binder et al,

[54] APPARATUS FOR FEEDING FIBER MATERIAL INTO A CI-IUTE [75] Inventors: Rolf Binder, Raterschen; Rudolf Wildbolz, Winterthur, both of Switzerland [73] Assignee: Rieter Machine Works, Ltd., Winterthur, Switzerland 22 Filed: Nov. 10,1969

21 Appl.No.: 875,094

[30] Foreign Application Priority Data 14 1 Jan.23, 1973 3,414,330 12/1968 Trutzschler ..l9/105CF 3,070,847 1/1963 Schwab ...l9/l05 CF 3,514,159 5/1970 Labbe ..302/59 FOREIGN PATENTS OR APPLICATlONS 3,925,426 1964 Japan ..l9/l05 CF The fiber material is directed onto one or more chutes Nov. 8, 1968 Switzerland ..16770/68 from a pneumatic transporting duct by rotatable cylint ders. Each chute has a cylinder associated therewith "3 9/ 302/29 which at least partially interrupts the transporting air [51] Int. Cl ..B65g 53/40 stream to intercept and direct a portion of the air flow [58] Field of Search 19/105 CF; 302/28, 59 andaentmined fib into the chute The cylinders may I be positively rotated or freely mounted. The cylinders [561' References C'ted are also mounted close to the back wall of the chute "UNITED STATES PATENTS to allow removal of accumulations of fibers on the cylinders. 3,157,440 1l/l964 ,l-lijiya etal. ..302/2s 2,512,523 6/1950 Fisher et a1. ..l46/253 x 22 Claims, 5 Drawing Figures 19 2o 26 19 20' 2s 19 I v-- D D 0 1 l c 24 v 25 24 Pmmfnmzaim 3,712,682

SHEETEUFZ INVENTORS 9 LF BINDER R 001.;- W/LDBOLZ 2 1 7770: EEYS APPARATUS FOR FEEDING FIBER MATERIAL INTO A CHUTE It has been known to utilize pneumatic flock transporting systems in which fiber material is pneumatically transported in flock form through a duct by means of a carrier medium, e.g., an air stream. Also, in many cases, it has been known to guide part of the fiber material from above and to deposit the material into one or more pressurized chutes which branch from the common transporting duct.

However, in order to supply a desired quantity of fiber material continuously by means of a pneumatic flock transporting system into a chute, the flocks must be deflected from the flock carrying air stream into the chute. For example, it has been known in an automatic carding room to use a nose-shaped deflecting element which is adjustably arranged and inclined upwardly into the transporting duct from the back wall of the chute, as seen in the direction of the material flow. A disadvantage of this device is, however, that fibers of the incoming fiber flocks adhere to the deflecting element causing fiber accumulations or entanglements on the element which impair the undisturbed separation into the feed chute of the fiber flocks supplied later. This eventually results in an uneven deposition in the chute.

' Other deflecting elements are also known which are arranged in the chute inlet opening as reflectors and which are provided with a straight surface extending across the transporting air stream into the upper part of the chute. The fiber flock carrying air stream is divided by such deflecting elements into part air streams which flow past the deflecting element fromabove and below and which join again behind the elements. Such deflecting elements are advantageous in that fiber entanglements or accumulations are prevented by the straight form of the surface facing the incoming fiber flocks, but, as the part air stream drag fiber flocks along, uniform fiber flock deposition in the chute is not ensured.

Accordingly, it is an object of the invention to ensure disturbance freesupply of pneumatically transported fiber material to a chute.

' It is another object of the invention to obtain uniform deposition of fiber material in flock form in a chute of a pneumatic flock transporting system.

It is another object of the invention to prevent formation of fiber entanglements about the deflecting elements of a chute feeding device.

Briefly, the invention provides an apparatus, for example, for spinning machines, for supplying fiber material in flock form from a pneumatic flock transporting system consisting of a pressurized duct for transporting fiber flock carrying air into a chute branching off from the duct. The apparatus includes a deflecting element defined by a smooth surfaced cylinder which is rotatable about a longitudinal axis and which is disposed at the branch .of the chute from the duct.

' In one embodiment, the cylinder is mounted with a slight clearance from the back wall of a chute and extends into the transporting duct to deflect a substantial portion of the fiber flocks into the chute.

In another embodiment where a plurality of chutes are connected to the transporting duct, each chute is provided with a deflecting cylinder. As above, each cylinder is slightly spaced from the back wall of the chute. Further, each succeeding cylinder can be mounted to project further into the transporting duct than the preceeding cylinder so as to compensate for reductions in pneumatic pressure from one chute branch off point to the next.

Thechutes may be formed with curvilinear back walls which are disposed to the rear of the cylinders with respect to the air flow or may be formed with straight walls with the cylinders arranged directly above the walls. In the latter instancefthe walls can be provided with adjustable separator heads which serve to adjust the spacing between the cylinders and walls. Further, in some embodiments, the separator heads can be fixed to the cylinders and the cylinders can be adjustably mounted with respect to the chute walls. In such instances, the space between a separator head and cylinder will remain constant as the cylinder is adjusted to project more or less into the transporting duct.

The cylinders can be positively driven or freely mounted for rotation. Also, the cylinders can be axially mounted or eccentrically mounted. '7

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a schematic longitudinal section of a portion of a transporting duct with a chute branching off incorporating a deflecting cylinder according to the invention;

FIG. 2 illustrates a schematic longitudinal section of a portion of a common transporting duct with a plurality of individual chutes utilized with a plurality of deflecting cylinders according to the invention;

FIG. 3 illustrates a schematic longitudinal section of a portion of a transporting duct with parallel neighboring feed chutes and deflecting cylinders of the invention in a fiber flock blending machine;

FIG. 4 illustrates a fragmentary perspective view of an alternative separator head according to the invention; and

FIG. 5 illustrates an alternative of the arrangement shown in FIG. 3.

Referring to FIG. 1, a connecting piece 2 is inserted into, and by means of outwardly directed flanges 4 and 5 connected to, a pressurized transporting duct 1 through which a fiber flock carrying air stream flows in the direction of arrow A originating from a machine (not shown) delivering fiber flocks. A' rectangular chute 6 is connected to the connecting piece 2 by means of a similar flange 7 in such manner that the chute front and back walls 8, 9 extending across the transporting duct 1 are the wider walls of the rectangular chute 6. The chute 6 can lead to any type of device for further processing, transporting or taking up of the fiber flocks, such as cards, openers, cleaners, conveyor belts, chambers the lower ends of which are open or provided with take-off rolls. The cross sectional area of the connecting piece 2 widens immediately behind the connecting flange 4 with the lower wall 10 being slightly inclined downwardly relative to the duct 1 and, via a curvature l1, merging into the front chute wall 8 of the chute 6. The back wall 9, as seen in the direction of the material flow, of the chute 6 extends upwardly to a somewhat higher position or elevation than the front chute wall 8 and at the upper edge 12 is bent into the direction of the material flow. A subsequent curvilinear section 13 is curved so far upwardly that a following section 14 of the lower wall is slightly inclined downwardly towards the connecting flange 5.

A deflecting cylinder 16 is arranged in the connecting piece 2 at the branch off point of the chute 6 and is mounted to rotate about its longitudinal axis 15. This longitudinal axis 15 is coplanar with the plane determined by the back chute wall 9 of the chute 6. The cylinder 16 is provided with a smooth surface and extends across the direction of the material flow, i.e., transversely of the duct 1, over the full inside width (not shown) of the back chute wall 9 and is provided with a drive mechanism which rotates the cylinder 16 in the direction indicated by the arrow B. Since such a drive mechanism would be of any suitable known construction, such need not be further described. If an airstream carrying fiber flocks flows in the direction indicated by the arrow A through the transporting duct 1 into the connecting piece 2, part of the incoming fiber flocks is deflected by the cylinder 16 arranged across the direction of the material flow and is guided into chute 6. The remainder of the air stream and fiber flocks flows on above the cylinder 16 into the transporting duct 1 continued behind the connecting piece 2 and is transferred either to a further chute connected to transporting duct 1 or is fed back to the machine supplying the fiber flocks. Should any fibers adhere to the cylinder 16 while fiber flocks are deflected into chute 6 such are brought out of the impact zone of the flocks by the rotation of the cylinder 16 in the direction indicated by the arrow B, are carried downward and drop into the chute 6. Owing to the rotation of the cylinder 16, the incoming fiber flocks always contact a fiberfree surface of the cylinder 16. As the fibers adhering to the surface of the cylinder 16 are carried away, fiber accumulations or similar inconveniences are avoided and free passage of the fiber flocks into the chute 6 is ensured at all times.

In order to avoid penetration of the fiber flocks reaching the upper edge 12 of the chute wall 9 between the upper edge 12 and the cylinder 16 into the room behind the cylinder 16, and thus to avoid clogging and impairing of the free rotatability of the cylinder 16 by fiber accumulations, the clearance between the cylinder surface and the upper edge 12 of the chute wall 9 is kept small. A large clearance would permit passage of fiber flocks which would cause considerable fiber entanglements at this place. The clearance is determined by free rotation of the cylinder 16.

In order to prevent disturbances, the curved wall section 13 of the connecting piece 2 adjacent to the upper edge 12 diverges from the surface of the cylinder 16 to define a space in which the cross-sectional area gradually increases. As a result, should any fiber flocks penetrate into the space defined between the curved wall section 13 and the surface of the cylinder 16 such are eliminated by the air stream flowing above the cylinder 16 and carried into the transporting duct 1.

Referring to FIG. 2, a transporting duct 19 can be provided with more than one chute as above. For example, two connecting pieces 20, 20 are inserted consecutively and connected to the transporting duct 19 by means of flanges 24, and 24, 25 respectively, and

are connected to chutes 22, 23 respectively which in turn can, as described earlier, supply the fiber flocks to any type of device (not shown) for further processing, transporting or taking up of the fiber flocks. The connecting pieces 20, 20 are designed in the same manner as the connecting piece 2 shown in FIG. 1 and are provided with rotatable cylinders 26, 26 respectively. The surfaces of the cylinders 26, 26' are smooth and are arranged in the same manner as cylinder 16 shown in FIG. 1 as a deflecting element above the upper edges 21, 21' respectively of the back chute walls.

The front and back walls of the chutes 22, 23 are also provided with perforations 22' 23' on both sides, through which a part air stream deflected from the transporting air streamby either of the respective cylinders 26, 26' and passing into a respective chute 22, 23 escapes into exhaust ducts (not shown) from where the air is eliminated in known manner. In this arrangement, the flocks are separated from the part air stream passing into the feed chute and escaping through the perforated walls, are deposited in the respective chute and furthermore are condensed by the pressure prevailing in the transporting duct 19.

A fiber flock carrying air stream originating from a machine for supplying fiber flocks (not shown) and flowing through the transporting duct 19 in the direction indicated by the arrow C is successively divided into part air streams in the connecting pieces 20, 20'. These part air streams, together with the fiber flocks are deflected into the corresponding chutes 22, 23 by the cylinders 26, 26' respectively. The cylinders 26, 26 which rotate in the directions indicated by the arrows D, D respectively and are driven by a drive mechanism (not shown) act as stream deflecting elements and ensure that the fibers adhering to the cylinder surfaces are carried away from the zone of fiber flock impact in the direction of the respective chute 22, 23. The fibers adhering to the cylinders 26, 26' and carried away from the impact zone by rotation of the cylinders 26, 26' furthermore are torn off the cylinder surfaces by the part air streams.

In order to achieve proper successive separation of each part airstream from the transporting air stream as air throughput diminishes in the transporting duct 19, cylinder 26' is set at a higher elevation in the duct 19 than cylinder 26. The air flow cross-sectional area at this place is thus smaller and uniform distribution of the incoming flocks into the respective chutes 22, 23 is achieved. Further, the clearance between the surface of the cylinder 26' and the upper edge 21 of the back chute wall of the rear chute 23 is the same as between the surface of the cylinder 26 and the upper edge 21 of the back chute wall of the forward chute 22 in order to prevent penetration of fiber material for reasons as described above. In this regard, the clearance can be achieved by any suitable means for maintaining the clearance.

Should additional chutes be connected to the transporting duct downstream of the connecting piece 20, for example, by means of connecting pieces equipped in the same manner, the subsequent cylinders (not shown) also are set successively higher for the reasons cited above from one chute to the next. In this case, the clearance between the cylinder surfaces and the upper edges of the corresponding chute walls are also kept constant as mentioned above.

After deflection of a part air stream into the last of a series of feed chutes connected to the common transporting duct 19, the transporting air stream either can, as mentioned earlier in the description of FIG. I, be fed back to the machine supplying fiber flocks or the whole fiber flock carrying air stream still remaining in the transporting duct 19 can be taken off in a known manner into a last chute into which the transporting duct finally merges.

Referring to FIG. 3, the deflecting elements can also be used with pressurized transporting duct 32 containing a fiber flock carrying air stream which merges into a plurality, of successively arranged parallel feed chutes 27 31 (shown partially) of a fiber flock blending machine (not shown). These feed chutes 27 31 are separated by their corresponding common walls 33 36 and are arranged in a housing 37 in which a distribution room extending above the individual chutes is provided. The feed chutes are provided with perforated side walls (not shown in the longitudinal section) while the chute end walls 39, 40 form the walls of the housing. A fiber flock blending machine of a similar type is described e.g., in US. Pat. Application Ser. No. 810,500, filed Mar. 26, 1969.

A cylinder 45, 46, 47, 48 is disposed above the upper edges 41, 42, 43, 44 of the individual chute walls 33 36 respectively and each is provided with a smooth surface. and is rotatably arranged at an adjustable height above the corresponding chute wall. The incoming flocks carried in the air stream via transporting duct 32 are distributed uniformly into the individual chutes 27 31 with the transporting air stream in the distributing room 38 above the chutes being successively separated into part air streams, as indicated by the arrows, by

means of the deflecting cylinders 45 48 which are set successively higher from chute to chute. Any fibers adhering to the surfaces of the cylinders 45 48 are carried away from the impact zone of the incoming fiber flocks owing to the rotation of the cylinder in the direction indicated by the arrows E and are taken off by the part air streams flowing into the chutes. The incoming flocks thus always contact a fiber-free surface of the cylinders so that fiber accumulations and entanglements on the deflecting elements, and thus at the chute entrance, are prevented. The cylinders are activated by a drive mechanism (not shown).

In order to maintain the clearance between the surfaces of the cylinders 45 48 and the corresponding upper edges of the chutes 33 36 constant, U-shaped separator heads 49 52 the height positions of which are adjustable, are provided on the upper edges 41 44 of the corresponding chute walls. In this way, the upper end of the chute walls 33 36 can beset at different heights.

Referring to FIG. 4, in order to obtain a simultaneous height adjustment of a cylinder and a separator head mounted on the upper portion of a chute wall 53, the U-profiled separator head 54 is disposed over the chute wall as in FIG. 3. Further the separator head 54 is pro.- vided on one side wall with a holder 58 which extends above the upper edge 56 of the separator head 54 and cooperates with a similar holder on the opposite side of the head 54 to support a shaft 60 of a cylinder 61 in the upper part. The shaft 60 is connected to a drive motor 59 so that the cylinder 61 can be rotated on an axis disposed at a distance F from the upper edge 56. The

distance F is chosen such that fiber flocks are sufficiently sealed off from penetrating between the smooth surface 62 of the cylinder 61 and the upper edge 56 of in a guide slot 63 of the holder58 and is connected to a threaded rod 56 disposed longitudinally of the chute wall 53. By turning the threaded rod 66, the separator head 54 is lifted or lowered vertically while the height position of the cylinder 61 changes simultaneously so that the distance F remains unchanged.

Referring to FIG. 5, the smooth surface cylinder 67 70 can also be mounted eccentrically above the chute walls 71 74 of a plurality of chutes 75 79. In this arrangcment, the incoming fiber flockscarried in an air stream through a transporting duct meet a surface of the deflecting element, the position of which surface constantly changes as the cylinder is rotated. As a result, the air current conditions on the cylinder surface change during rotation. This favorably influences the taking off of fibers adhering to the cylinder surface.

The eccentricity of the cylinders 67 70 can be of a value corresponding about the distance between the cylinder surface and the upper edge of the chute. Preferably the eccentricity is such that a penetration of fiber flocks is avoided between the upper edge 49, 50, 51, and 52 and the cylinder 45, 46, 47, and 48 and the cylinder can rotate freely. In order to avoid, for example,.inconvenient pneumatic or mechanical vibrations in the system the eccentricity of the cylinders can be transposed each to another by or It is noted that where a plurality of cylinders are arranged, one each at successive branching points of feed chutes, the cylinders can be driven in phase or out of phase as needed or desired on the circumstances prevailing. Thus, it is possible to rotate e.g., the first two cylinders shown in FIG. 3 counterclockwise and the following two cylinders clockwise if needed for effecting current conditions favorable for uniform distribution of the incoming fiber flocks and for successively separating part air streams from the transporting air stream.

Furthermore it is possible to rotate at least two cylinders in an opposite direction each to another. It is also possible where a plurality of cylinders are arranged one each can be driven with a speed different from the other or a pair of cylinders can be driven with a speed different from the speed of another pair of cylinders.

Preferably the number of revolutions of the cylinders is of about 50 200 r.p.m., but lower or higher revolutions can be applied.

The deflecting cylinders also can be arranged to be freely rotatable without a drive mechanism such to be rotated by the air stream flowing above them. In this case, all of a plurality of cylinders arranged in sequence are rotated in the same direction.

. If the cylinders shown in FIGS. 3 or 5 are driven clockwise or if they are freely supported and rotated by the transporting air stream, fibers adhering to the cylinder surfaces are carried away from the impact zone of the incoming fiber flock carrying air stream into the region of the transporting air stream flowing above the cylinders where they are taken off from the cylinder surface by the transporting air stream flowing tangentially across the cylinder surface.

What is claimed is:

1. In a combination with a pneumatic transporting duct for transporting fiber flock carrying air and at least two chutes connected with said duct for individually receiving at least a part stream of the fiber flock carrying air, each said chute having a back wall with respect to the direction of air flow in said duct; means disposed at the branching of each of said chutes from said duct and extending into a partial portion of said duct for deflecting a part stream of the fiber flock carrying air from said duct into each respective chute while defining an air flow cross-sectional area with said duct for the remainder of the carrying air, each said means defining a smaller air flow cross-sectional area with said duct at a downstream chute of said chutes than at an upstream chute; each said means including a rotatably mounted deflecting element cylinder having a smooth surface disposed above a respective back wall with an axis disposed in the plane of said back wall, each said cylinder being closely spaced to a respective back wall to avoid clogging and impairing of the rotatability of said cylinder by fiber accumulations.

2. The combination as set forth in claim 1 wherein said cylinder is disposed across the direction of the flow of air in said duct.

3. The combination as set forth in claim 1 which further comprises a drive mechanism connected to said cylinder for rotating said cylinder about the longitudinal axis thereof.

4. The combination as set forth in claim 1 wherein said cylinder is rotatably supported in the axis of rotational symmetry thereof.

5. The combination as set forth in claim 1 wherein said cylinder is rotatably supported eccentrically.

6. The combination as set forth in claim 1 wherein said cylinder has a longitudinal axis of rotation disposed in the plane of said back wall.

7. The combination as set forth in claim 1 wherein said cylinder extends across the entire width of said chute back wall.

8. The combination as set forth in claim I wherein said cylinder is adjustably mounted above said back wall.

9. The combination as set forth in claim 1 wherein said back wall has a height adjustable upper edge.

10. The combination as set forth in claim 9 wherein said cylinder has a longitudinal axis of rotation spaced from said upper edge of said back wall to maintain a constant space between said cylinder and said back wall.

1 1. The combination as set forth in claim 10 wherein said upper edge of said back wall and said cylinder are simultaneously adjustable in height.

12. The combination as set forth in claim 1 wherein said chute has lateral perforated walls for the passage of air therethrough.

13. The combination as set forth in claim 1 wherein said cylinders are rotatably driven in phase.

14. The combination as set forth in claim 1 wherein said c qjnders are rotatably driven out of phase.

15. he combination as set forth in claim 1 wherein at least two chutes are adjacent each to the other.

16. The combination as set forth in claim 1 wherein at least a pair of chutes have a common non-perforated smooth separating wall therebetween.

17. In a pneumatic flock transporting system as set forth in claim 1 wherein a connecting piece is connected between said duct and each respective chute, each said cylinder being mounted within a respective connecting piece across said chute.

18. In a pneumatic flock transporting system as set forth in claim 17 wherein said connecting piece is of in creasing cross-sectional area with respect to the flow of fiber carrying air upstream of said respective chute and of increasing cross-sectional area with respect to the flow downstream of said respective chute.

19. The combination as set forth in claim 1 wherein at least two cylinders rotate in an opposite direction.

20. The combination as set forth in claim 1 wherein at least two cylinders rotate with a different speed.

21. The combination as set forth in claim 1 wherein each said back wall extends upwardly to a higher position than a front wall of respective chute.

22. The combination as set forth in claim 1 wherein each said back wall of respective chute is bent at the upper edge into the direction of the flow in the duct and is curved upwardly diverging from said cylinder.

l i i i i 

1. In a combination with a pneumatic transporting duct for transporting fiber flock carrying air and at least two chutes connected with said duct for individually receiving at least a part stream of the fiber flock carrying air, each said chute having a back wall with respect to the direction of air flow in said duct; means disposed at the branching of each of said chutes from said duct and extending into a partial portion of said duct for deflecting a part stream of the fiber flock carrying air from said duct into each respective chute while defining an air flow cross-sectional area with said duct for the remainder of the carrying air, each said means defining a smaller air flow crosssectional area with said duct at a downstream chute of said chutes than at an upstream chute; each said means including a rotatably mounted deflecting element cylinder having a smooth surface disposed above a respective back wall with an axis disposed in the plane of said back wall, each said cylinder being closely spaced to a respective back wall to avoid clogging and impairing of the rotatability of said cylinder by fiber accumulations.
 2. The combination as set forth in claim 1 wherein said cylinder is disposed across the direction of the flow of air in said duct.
 3. The combination as set forth in claim 1 which further comprises a drive mechanism connected to said cylinder for rotating said cylinder about the longitudinal axis thereof.
 4. The combination as set forth in claim 1 wherein said cylinder is rotatably supported in the axis of rotational symmetry thereof.
 5. The combination as set forth in claim 1 wherein said cylinder is rotatably supported eccentrically.
 6. The combination as set forth in claim 1 wherein said cylinder has a longitudinal axis of rotation disposed in the plane of said back wall.
 7. The combination as set forth in claim 1 wherein said cylinder extends across the entire width of said chute back wall.
 8. The combination as set forth in claim 1 wherein said cylinder is adjustably mounted above said back wall.
 9. The combination as set forth in claim 1 wherein said back wall has a height adjustable upper edge.
 10. The combination as set forth in claim 9 wherein said cylinder has a longitudinal axis of rotation spaced from said upper edge of said back wall to maintain a constant space between said cylinder and said back wall.
 11. The combination as set forth in claim 10 wherein said upper edge of said back wall and said cylinder are simultaneously adjustable in height.
 12. The combination as set forth in claim 1 wherein said chute has lateral perforated walls for the passage of air therethrough.
 13. The combination as set forth in claim 1 wherein said cylinders are rotatably driven in phase.
 14. The combination as set forth in claim 1 wherein said cylinders are rotatably driven out of phase.
 15. The combination as set forth in claim 1 wherein at least two chutes are adjacent each to the other.
 16. The combination as set forth in claim 1 wherein at least a pair of chutes have a common non-perforated smooth separating wall therebetween.
 17. In a pneumatic flock transporting system as set forth in claim 1 wherein a connecting piece is connected between said duct and each respective chute, each said cylinder being mounted within a respective connecting piece across said chute.
 18. In a pneumatic flock transporting system as set forth in claim 17 wherein said connecting piece is of increasing cross-sectional area with respect to the flow of fiber carrying air upstream of said respective chute and of increasing cross-sectional area with respect to the flow downstream of said respective chute.
 19. The combination as set forth in claim 1 wherein at least two cylinders rotate in an opposite direction.
 20. The combination as set forth in claim 1 wherein at least two cylinders rotate with a different speed.
 21. The combination as set forth in claim 1 wherein each said back wall extends upwardly to a higher position than a front wall of respective chute.
 22. The combination as set forth in claim 1 wherein each said back wall of respective chute is bent at the upper edge into the direction of the flow in the duct and is curved upwardly diverging from said cylinder. 